A conventionally known boiler system including a boiler that burns fuel such as coal, heavy oil, or biomass includes a denitration device that removes nitrogen oxide (NOx) contained in a combustion gas exhausted from the boiler, and a desulfurization device that removes sulfur oxide (SOx) contained in the combustion gas.
In many of such boiler systems, a denitration device, an electrostatic precipitator, and a desulfurization device are arranged in this order from a side of the boiler. Also, as a denitration device, which is often used that sprays ammonia (NH3) into a combustion gas generated by burning to reduce nitrogen oxide in the combustion gas.
However, if the denitration device that uses ammonia as a reagent is arranged on an upstream side of the desulfurization device, a large amount of sulfur oxide is mixed in the combustion gas flowing into the denitration device. In this case, in the denitration device, the sulfur oxide and the ammonia in the combustion gas react to generate acid ammonium sulfate (ammonium hydrogen sulfate: (NH4)HSO4). Accumulation of ash in a flow path or a device on a downstream side of the denitration device caused by the acid ammonium sulfate prevents passage of the combustion gas and increases pressure loss. Also, the sulfur oxide contained in the combustion gas reacts with metal to corrode the metal. Further, the acid ammonium sulfate produces condensable particulates (for example, particulate matter referred to as PM2.5).
Also, if the electrostatic precipitator is arranged on the downstream side of the denitration device, impurities such as smoke dust are mixed in the combustion gas flowing into the denitration device. The impurities adhere to a catalyst provided in the denitration device and thus deteriorate the catalyst, thereby reducing the life of the denitration device.
PTL 1 proposes a boiler system in which an electrostatic precipitator, a desulfurization device, and a denitration device are arranged in this order from a side of a boiler. The boiler system described in PTL 1 can solve the problems described above because impurities such as sulfur oxide or smoke dust are removed from a combustion gas introduced into the denitration device.
PTL 2 discloses a lean combustion engine that partially oxidizes and converts diesel fuel into carbon monoxide and hydrogen, and supplies the carbon monoxide and the hydrogen to a hydrocarbon selective catalystic reduction catalyst as reagents.
PTL 3 discloses a NOx reduction method for reducing nitrogen oxide by catalyst action using a hydrocarbon reagent.
PTL 4 discloses an exhaust gas treatment catalyst that supports Ir and other metals in an alloy state on a carrier.
PTL 5 discloses a device in which a desulfurization device, smoke dust collection means, and a denitration catalyst are arranged in this order from a side of the engine.